1. Field of the Invention
The present invention relates generally to ionospheric delay measurements, and in particular, to a method, apparatus, and article of manufacture for generating high-precision ionospheric delay measurements to serve as ground-truth for the Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) algorithm development and validation. Embodiments of the invention may provide an average of thirty percent (30%) improvement in data volume over the prior art.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by reference numbers enclosed in brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Global Positioning System (GPS) is a satellite navigation system used to determine one's precise location and provide a highly accurate time reference almost anywhere on Earth or in Earth orbit. However, GPS measurements may have errors based on various causes. The ionosphere is one of the leading causes of GPS measurement error. In this regard, ionospheric storm conditions may cause significant ionospheric delays to occur. The Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) may be used to improve the accuracy and integrity of information coming from GPS satellites. In WAAS, ground stations receive the GPS signals and transmit a corrective signal to account for GPS measurement errors. However, during increased solar activity, significant portions of data that is highly critical for creating the corrective signal is missing. The prior art fails to provide a mechanism for determining and utilizing the missing data. These deficiencies of the prior art may be better understood with a description of WAAS and the missing data.
WAAS is a system of satellites and ground stations that provide GPS signal corrections to provide better position accuracy. WAAS consists of approximately twenty-five (25) ground reference stations positioned across the United States that receive/monitor GPS satellite data. The ground reference stations transmit the GPS satellite data (e.g., via a terrestrial communication network) to two master stations (located on both coasts), that create a GPS correction message (also referred to as an augmentation message). The correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere.
The correction message is uplinked to geostationary communication satellites for transmittal/broadcast to WAAS enabled receivers that collect the GPS signals and remove errors in the GPS signals using the corrective information.
Unfortunately, currently existing data sets (provided by the receiving stations) for providing high precision ionospheric delay measurements during ionospheric storm conditions show significant portions of data missing during increased solar activity. This portion of data is highly critical for high precision ionospheric threat model development needed to increase WAAS availability and integrity during ionospheric storm conditions.